A Sleep Apnea Monitoring IC for Respiration, Heart-Rate, SpO2 and Pulse-Transit Time Measurement Using Thermistor, PPG and Body-Channel Communication.

This paper presents a low power bio-signal acquisition system for sleep apnea, which can measure respiration, heart rate, SpO2, and pulse transit time (PTT). For respiration, a nasal airflow sensor with a thermistor is used. For PTT that can serve as a surrogate for blood pressure during sleep, two photoplethysmogram (PPG) sensors are employed at the upper arm and the finger. For improved comfort during sleep, body channel communication (BCC) is used to remove long wires. To reduce power consumption and circuit complexity, sensor’s analog front-end is implemented by using a current-controlled oscillator which is also shared by BCC transmitter that employs analog frequency modulation. Implemented in $0.18~\mu \text{m}$ CMOS, the proposed IC consumes less than 3.6 mW from a 1.8 V supply, while occupying 0.145 mm2 of active area. [ABSTRACT FROM AUTHOR]